The present invention is directed to staging compressors in a multi-compressor multi-circuited refrigeration system, and more particularly, to determining which compressors to stage on and off and which compressors to modulate in a multi-circuited refrigeration system where each circuit is associated with more than one compressor.
In a multi-compressor refrigeration system it is desirable to equalize compressor wear between all of the operating compressors Two significant components of compressor wear are a compressors accumulated run time and the number of starts a compressor has experienced. Thus, a staging scheme that starts a compressor based on the lowest number of starts and stops a compressor based on the greatest accumulated run time will tend to equalize these components of compressor wear. Such a scheme is described in U.S. Pat. No. 5,123,256 which is assigned to the assignee of the present invention and hereby incorporated by reference The system shown in this patent has a single refrigeration circuit with a plurality of compressors associated with that circuit The system of this patent works well with single circuited refrigeration circuits and with systems having a one-for-one correspondence between compressors and refrigeration circuits. However, in a system having multiple refrigeration circuits with multiple compressors associated with each circuit, it is desirable to spread the system capacity over all of the refrigeration circuits so as to maximize the heat exchange surface area, and it is also desirable to optimize compressor modulation on each refrigeration circuit.